The problem of aerosols and gas propellants causing harm to the ozone layer has been widely debated in science and industry and many attempts have been made to find effective, economical alternatives.
The propellant gas which causes no atmospheric pollution and which would therefore provide the ideal solution, namely, air, cannot be maintained under sufficient pressure in an aerosol can during storage and use. Thus, other solutions have been proposed which resolve the user's immediate problems, but are far less satisfactory from the point of view of economics and ecology. The problem to be overcome is that of maintaining a reserve of pressure in a can which is sufficient to allow the entire can contents to be sprayed out and used. Propellant gases presently in use are methane, propane, etc. These gases are flammable or even explosive when mixed with a certain proportion of air and can therefore be dangerous to use.
Furthermore, from an economic point of view, such use wastes energy, since it is certainly preferable to utilize these combustible gases as energy sources rather than as propellants freed into the atmosphere. Finally, these gases generally cannot be mixed with the can contents and must be sealed into flexible pouches made of aluminum, synthetic material or a very thin film of composite material.
A more satisfactory solution is to recharge the aerosol can with compressed air when pressure in the can is no longer adequate to propel the substance from the can.
Various devices are known for pressurizing aerosol cans, specifically in German Publication No. DE-A-3 800 194 and Utility Model DE-U-8 808 407.
German Publication DE-A-3 800 194 describes an aerosol can pressurizing device using a compressor consisting of a fill nozzle and a switch. The problem with this device is that it provides neither a means for attaching it to the aerosol can nor a means for controlling pressure inside the can. The user must hold the can in place manually by pressing it downward to engage the fill nozzle with the flow control valve on the aerosol can and thus keep the valve open during the filling process. The user must then remove the aerosol can when he or she estimates that there is adequate interior pressure in the can to spray out the contents, that is, neither too high nor too low, which can be dangerous.
The device described in Utility Model DE-U-8 808 407 consists of a frame with a compressor which has a reservoir of compressed air, a fill nozzle and an upper arm. When the aerosol can is engaged with the housing provided in the frame, the upper arm presses the can downward. This causes the flow control valve located in the can base and engaging the fill nozzle to open, which places the compressed air reservoir in contact with the inside of the can. Pressure in the air reservoir and inside the can reach an equilibrium. This can has several flaws. It is particularly large and therefore impractical. In addition, because of the fact that it has an upper arm and the way this functions, only cans of a certain height can be used. Another problem with this device arises because the inside of the can remains in contact with the reservoir of compressed air as long as the can remains on the support. Here again, the user must remove the can from the support when he or she estimates that the desired interior pressure has been attained.
In sum, these present solutions are dangerous, expensive, polluting and impractical, and thus wholly unsatisfactory.